Measure a QSY spot from where the call was first seen

The radio reports the frequency in small steps as the knob turns, and
each step was compared with the one before, so no step passed the
threshold. The move is now measured from the frequency the radio had
when the call appeared in the entry window. The threshold is a box on
the Filters tab of the telnet window.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/Nonemm.App/Windows/TelnetWindow.axaml

@@ -122,6 +122,8 @@
           <TextBox Name="BlockedCallsBox" />
           <TextBlock Classes="label" Text="Bandmap spot timeout (minutes)" />
           <TextBox Name="TimeoutBox" Width="60" HorizontalAlignment="Left" />
+          <TextBlock Classes="label" Text="Spot a call locally when the radio moves more than (Hz)" />
+          <TextBox Name="QsySpotBox" Width="60" HorizontalAlignment="Left" />
           <Button Content="Apply" Click="OnApplyFilters" Margin="0,10,0,0" />
         </StackPanel>
       </ScrollViewer>